Oklahoma executioners failed to place an injection line properly in a vein in the groin of Clayton D. Lockett, according to an independent autopsy commissioned by Mr. Lockett’s defense lawyers after his bungled execution drew wide attention to the problems of lethal injection.

The finding, released Friday, may explain why Mr. Lockett was not completely sedated, then writhed and moaned in apparent agony before dying of heart failure 43 minutes after the procedure began.

The finding contradicts the claim by Oklahoma prison officials that Mr. Lockett’s vein had collapsed or “blown,” as one described it. Instead, the new report indicates that Mr. Lockett’s femoral vein, located deep below the surface of the groin, was punctured by inexpert probing and that the execution drugs were not pumped directly into the bloodstream.

The state commissioned an autopsy, sending Mr. Lockett’s body to the Southwestern Institute of Forensic Sciences in Dallas for examination, but the results have not been released. Gov. Mary Fallin also asked the chief of public safety to conduct a broad review of what went wrong on April 29 and whether execution procedures should be overhauled.

A spokesman for Ms. Fallin, Alex Weintz, said that the official review continued and that while officials had not seen the independent autopsy report, “it seems to verify what we already knew — there was a problem administering the IV.”

In their initial public accounts, Oklahoma officials described a hectic scene at the state prison’s execution chamber. A medication technician spent nearly an hour trying, without success, to place a catheter in Mr. Lockett’s arms and legs or feet.

Then, on the advice of an attending physician whose precise role remains unclear, the team sought to insert the needle through the groin into a femoral vein — a far more difficult and painful procedure, often done in hospitals with the aid of an ultrasound machine, since the vein is not otherwise visible.

The team apparently believed that it had succeeded in placing the line. But from the beginning, things did not proceed normally. According to witnesses, Mr. Lockett was unusually slow to become unconscious after injection of a sedative, the first in a three-drug combination that was being tried in Oklahoma for the first time.

Once the attending physician declared Mr. Lockett unconscious, officials injected a paralyzing agent and a drug intended to stop his heart, but he appeared to wake up, witnesses said, and bucked against his restraints and mumbled before prison officials drew the curtain on the witnesses.

Failure of the intravenous line is consistent with the observed events, medical specialists said, and also suggests the possibility of suffering. With a catheter deep in the groin, but not feeding into an intact vein, the drugs would have spread through local tissue and been only partially absorbed into the bloodstream. Thus it appears that Mr. Lockett was not completely sedated and then partially paralyzed before receiving an incomplete dose of the painful heart-stopping agent, potassium chloride.

The independent autopsy was performed by Dr. Joseph I. Cohen, a forensic pathologist based in Novato, Calif., who was formerly chief forensic pathologist for Riverside County, Calif., and now runs an independent consulting firm, United Forensic Services. He saw the body in Tulsa on May 14, after the state-sponsored examination was completed in Dallas.

In the preliminary report, Dr. Cohen wrote that the presence of skin punctures revealed multiple efforts to place needles in the veins of Mr. Lockett’s extremities and both sides of his groin. He found, he wrote, “the presence of vascular injury indicative of failed vascular catheter access.”

The planned executions on April 29 of Mr. Lockett and another prisoner, Charles F. Warner, who has not yet been executed, had already been the subject of intense legal and news media scrutiny because the state was using a new drug combination and refused to divulge the manufacturers.

But the sequence of events that night, and Friday’s report, suggest that failed placement of the intravenous line, not the quality of the drugs, was the immediate problem.

According to state rules, the names of the medication technician and doctor involved are kept secret.

“Initial results of Clayton Lockett’s autopsy indicate extraordinary incompetence on the part of the execution team that was separate and apart from the drugs used,” Deborah Denno, a law professor at Fordham University and death penalty opponent, said Friday in a statement.

Mr. Lockett was condemned for the murder of a 19-year-old woman whom he was convicted of shooting and burying alive. The execution of Mr. Warner, convicted of the rape and murder of an 11-month-old girl, has been delayed indefinitely while the state investigates what went wrong and whether it should change its procedures.

A version of this article appears in print on , on Page A14 of the New York edition with the headline: Defense Reports Puncture Led to Botched Execution. Order Reprints | Today’s Paper | Subscribe